Process safety performance indicators are applied to monitor and improve the safety of process plants. One of the most important and challenging issues for process safety is the early recognition of deterioration in safety performance caused by operation, maintenance, management, organization, and safety culture factors before actual events and/or mishaps occur Most existing safety performance indicators are "lagging" indicators meaning that they monitor events after their occurrence. This article presents a risk-based approach to measure process safety using a set of safety performance indicators. This approach uses a risk metric as a means to classify process safety. Risk provides a common ground to integrate the two main indicator types of leading and lagging indicators. It is important to note that lagging and leading indicators have a relationship, which is often ignored. The proposed methodology is a structured approach, which builds upon UK's Health Safety Executive recommended process safety indicator development framework. At present, work efforts have been made to develop a set of indicators with a common background to measure process safety. This article demonstrates a hierarchical risk aggregation approach which is used to aggregate indictors. This work was carried out with the help of the Loss Prevention Division of Qatargas Operating Company Limited (Qatargas), a Liquefied Natural Gas (LNG) company. Finally, the applicability of the approach is demonstrated by a case study on a liquefied natural gas facility. The result of this study shows a relationship between the leading and lagging indicators which together contribute to the improvement of process safety performance. (C) 2009 American Institute of Chemical Engineers Process Saf Prog 29: 133-143, 2010